H. pylori infection causes chronic gastritis and peptic ulceration and is the strongest risk factor for the development of gastric cancer. H. pylori-initiated chronic gastritis is characterized by the enhanced expression of proinflammatory cytokines, whose expression is largely mediated by transcription factor NF- kappaB. Activation of NF-kappaB is tightly regulated by cytoplasmic and nuclear events, including the activation of IKK, the degradation of I(B( in the cytoplasm, and the various posttranslational modifications of NF-kappaB in the nucleus. H. pylori virulence factor CagA is injected into epithelial cells via the type 4 secretion system and has long been indicated to be critical for the H. pylori-mediated inflammatory response. H. pylori CagA elicits its various functions by interacting with different host signaling molecules, an event which requires the binding of CagA to the membrane and the oligomerization of CagA. Our recent studies demonstrate that CagA is essential for the H. pylori-induced activation of NF-kappaB and the inflammatory response. However, how the membrane binding and oligomerization properties of CagA contribute to the H. pylori-induced inflammatory response, how CagA hijacks cellular signaling molecules for the activation of NF- kappaB, and how the posttranslational modifications of NF-kappaB regulate the H. pylori-induced inflammatory response remain to be determined. This proposal seeks to explore these important questions. In Specific Aim 1, we will decipher the role of CagA membrane-binding and oligomerization properties in H. pylori-mediated NF-(B activation by examining various membrane-binding and oligomerization- defective mutants of CagA and H. pylori strains harboring these CagA mutants. We will also determine the in vivo function of these properties of CagA by infecting Mongolian gerbils with various H. pylori CagA mutant strains. In Specific Aim 2, we will define whether and how the intracellular host signaling proteins are hijacked by H. pylori virulence factor CagA for the activation of NF-kappaB. We will also determine whether blocking the interaction of CagA with host cell proteins represents an effective approach to inhibit the H. pylori-mediated inflammatory response. In Specific Aim 3, we will define the role of posttranslational modifications of RelA in H. pylori-induced NF-(B activation. In addition, we will assess the interplay between various posttranslational modifications and how these modifications function alone or in combination to control the H. pylori-mediated inflammatory response. Successful accomplishment of these Specific Aims will provide new insights into the role of CagA in the H. pylori-mediated activation of NF-kappaB and identify novel host signaling molecules hijacked by CagA, and will identify new therapeutic targets to mediate the NF- kappaB-dependent inflammatory response through inhibiting the interaction of CagA with host signaling molecules or by modulating the posttranslational modifications of NF-kappaB.